Although building of bridge type structures with prefabricated elements have been known for sometime and mainly used by the military no satisfactory system has so far been introduced which would serve the long felt need for a relative inexpensive system of bridge type structures which could be assembled within the existing rights of way and with little obstruction to traffic flow, and which could provide overpasses at crossings and elevated roadways.
Another long-felt need is for a quickly assembled structure to act as a temporary roadway or deviation while a main building project is in progress, and to be disassembled and ready for reuse, when no more required.
Presently such structures are built mainly on location with only a limited use of prefabricated elements, in relative long building times, sometimes obstructing traffic for periods of 12 months and more, and causing great losses to the businesses served by those obstructed roads. Sometimes, because of these obstructed roads, traffic adopts even entirely new patterns and does not return to these roads with their new and very costly overpasses.
Some modular systems have lately been developed and patented. These are mainly systems of precast concrete elements intended mainly for heavy type bridging and made up of a relative great number of elements. These have not been found to provide advantages, being mostly cumbersome in assembly and looks, and have therefore not found acceptance, especially as they do not provide complete systems.
It has been customary so far to build overpasses with conventional methods for carrying or deviating all the traffic at a great expense and long time periods causing great hardships to the general public. Even more the public is exposed to continuing hardships on roads without overpasses, especially where a national or a long distance highway passes through urban centers causing traffic to pile up at the crossings, adding unnecessary pollution and increased fuel consumption by idling engines. No system has so far been provided which could satisfactory serve to carry the traffic in a relative inexpensive way, in a constant flow over crossings and as elevated raodways, and to cut down traveling time, fuel consumption and pollution. No system has so far been introduced to carry the greater amount of road traffic composed of cars and vans only, although these make up over 80% of all traffic at most points, and the building of such lighter structures can be executed at a fraction of conventional costs, and the relative light structures can be built in a graceful form to find public acceptance for the important building of overpasses.